2024

Gilts are the Foundation for Productivity and Longevity

Gilt pool management is a critical issue for a successful pork farm.

by Mark E. Wilson

Gilts are the foundation of the herd, which allows it to have the best farrowing rates and to have a total of 14–15 pigs in their first litter.

Pigs weaned/sow/year performance (psy) gives comfort that we can look at production efficiency. See Table 1.

table showing impact of longevity over litter size
Table 1. Impact of longevity over litter size. Dan Bussieres, agr. B.Sc. Advances in Pork Production (2020) Volume 31, page 101s

Cost of Culling Replacement Sows

A focus on managing gilts is more likely to improve overall herd productivity than focusing on any other parities.

It is well understood that gilts need to make at least three litters to pay back the cost of replacing an older sow (Stalder et al., 2003).

To maximize a hog farm’s profits, gilt management requires the minimizing of non-productive sow days (NPD), successful pig flows beginning with gilts, reproductive success, sow longevity, and lactation performance.

Based on the PigCHAMP North American Database for females arrived in 2016-2020 the retention rate until parity 6, less than 30 percent of the females arrived in the period remained in the herd after their sixth parity. The biggest loss occurring between parity 1 and parity 2 ranged between 14.5-19.0 percent (Jennifer Patterson and Sergio Canavate, Benchmark, PigCHAMP, Spring 2023, pg. 25–29.)

Looking at a similar PigCHAMP North American database for gilts arriving between 2015-2022, 419,530 sows were removed between parity 1 and parity 2, the top reasons for removal (Figure 2) can be traced back to how gilts and gilt pools are managed.

graph showing removal reasons
Figure 2. Removal reasons between parity 1 and parity 2

Farms often have periods when they run short on gilts for targeted gilt pools.

When a swine farm is short on target numbers of quality gilts, they will often attempt to meet breeding targets with these three steps: 1) breed more opportunity sows and gilts; 2) retain sows that should be culled; and 3) keep marginally selected gilts since they lack adequate numbers of high-quality Grade 1 gilts.

When targeted goals of gilt flow are not met at a farm, they will stock up on more gilts of younger age and body weight, which don’t handle the stress and performance nearly as well.

It is recommended that farms should maintain 12–15 square feet for each gilt within a pen.

For example, a farm during the spring may run 15 gilts to each heat detection pen. When these pens become overstocked with gilts, these females will pay little attention to heat-check boars. In summer, hot weather decreases feed consumption, slowing the growth rate, which adds to the problem of gilt flow.

Increasing gilt numbers in the pen to 27 gilts under the same conditions will have a much poorer rate of heat detection.

Younger boars being crowded by the excess gilts often cause boars to minimize heat checking and want to exit the pen.

Arrival of Gilts onto a Farm

When purchasing gilts, the farm business always needs to plan ahead for enough time to allow for isolation, acclimatization, and a “cooling off period.”

As gilt numbers decline, managers often tend to bring more gilts into the breeding herd ahead of schedule. As such, here are a few rules to consider when introducing new gilts to the farm:

Strive to bring healthier animals into the herd;

Avoid introducing replacement animals directly into an established herd without an adequate “cooling off” period;

Follow the rules suggested by vaccination schedules. Typically, gilts should be vaccinated at least four weeks before starting with heat-no-service pens. Giving them a second shot 14 days after the first shot can give the gilt a much bigger boost on titers for the vaccinations recommended by veterinarians. Many farm systems also put gilts into a training program to give attention to what is called “crate breaking.” Also important is the electronic sow feeding station (ESF); it generally takes about two weeks to get the animals trained.

Gilt Selection and Structure

Gilt selection should encompass the whole body structure, evaluating leg and claw positions in gilts.

Locomotion issues with gilts that have incorrect leg structure and claw positioning can be a common reason for culling gilts and parity one sows. It is important to have a gilt with a level top line, as this helps set the legs with a better structure.

One should avoid gilts that have issues with rump slope (how much lower the tail is from the top line of the gilt).

When observing cull rows in sow farms, one would find that many more sows have a steep rump slope and poor posture with their rear feet too far forward.

It is important to have the claws line up straight forward on both the front and rear legs. A claw structure that turns outward or inward will result in joint issues in gilts.

An article in National Hog Farmer (Mark Knauer et al., February 6, 2020) points out excellent photos of the correct structure of gilts, as well as images of gilts that should be culled with buck-kneed and straight pasterns. It is important to have some flex in the pasterns in the front and rear legs.

It is important to identify gilts that have 14 to 16 nipples with equal spacing and prominent size. Gilts with irregular spacing of the nipples or missing nipples on their underline need to be culled before the final selection phase.

A category that has received more attention recently is gilt vulva size and functionality. Two items that need to be considered are gilts that have an infantile vulva (the vulva’s too small) and gilts that have a tipped-up vulva. These gilts need to be removed from breeding, sent to finishing growth, and then sent to market.

Recent research projects have evaluated the measurements of vulva width (VW), vulva length (VL), and vulva area (VA).

The first project focused mainly on vulva width, with 958 prepubertal replacement gilts in a commercial farm system evaluated.

The research team used four different methods to evaluate: vulva width, digital caliper (mm), visual evaluation, and scoring by trained farm personnel.

Vulva score A, S, M, L and 1, 2, 3.

Vulva score B was 1, 2, 3, 4, and 5 (Matthew Romoser et al., Transl. Anim Sci 2020, 4:275-284).

Gilts whose vulva area (VA) was within or greater than the standard deviation of the mean 66 percent and 79 percent exhibited estrus before 180 and 200 postnatal days, respectively (Kody L. Graves et al., Trans l. Anim. Sci. 2020. 4:285-292).

These data points support the utilization of VA changes between 95 and 115 days of age as a useful tool to identify replacement gilts prior to puberty for inclusion into the sow herd.

Gilt Eligibility at Mating

There are four general recommendations:

  • Early puberty: start boar stimulation early (approximately 170 days of age). More than 90 percent of gilts should have a recorded heat at 195–200 days.
  • Breed gilts on the second detected estrus. Delay on the third detected estrus if the sow’s body weight is less than 300 lbs. (~136 kg).
  • Breed gilts weigh between 308.7 and 352.7 lbs. (140 and 160 kg body weight). The authors suggest avoiding going beyond 355 lbs. (161 kg). (Jennifer Patterson and Sergio Canavate, Benchmark, PigCHAMP, Spring 2023, pg. 25–29.)
  • Breed gilts prior to 225 to 230 days without getting gilts overconditioned. A failure to select gilts with the greatest reproductive potential and inappropriate management of their physiological state and metabolic condition at service are key risk factors for poor sow life-time productivity (Patterson and Foxcroft, 2019).

Conditions of Buildings and Housing

If we look back 15 years or more, gilts were very often not considered a top priority.

The advent of building a sow farm sight away from the sow herd, called the gilt development unit (GDU), allowed for isolation, acclimation, and a cooling-off period before entering the breeding herd.

We have also added the issue of electronic sow feeding (ESF), which takes a few weeks of training to get the gilts to eat well at a training station.

We are pleased with advancements in paying more attention to our gilts. We still struggle with issues of lameness, poor locomotion, and putting enough selection pressure on the gilts.

We tend to find a lot of barn facilities that seem to have wet flooring—large amounts of manure in crates and/or flooring in pens.

There are some interesting studies that we can share from the dairy herds.

The degree of hardness of claws differs some between dairy cattle and sows. Both animal species will find that standing in water and manure will soften the horn tissues and may increase injuries.

When we see flooring that is wet and damp most of the day, we need to think about what the wet floor is doing to gilts and sows.

The heel and the sole of a pig are the tissues that show the greatest impact, with an estimated increase in water weight of 30 percent (Borderas et al., 2004). If the claws continuously get moisture and then dry out multiple times a day, the potential to cause lesions and locomotion issues is increased.

In pigs, the heel will soften even more than the sole. Softer heels and soles will increase the number of claw lesions and injuries.

Proper ventilation can aid in promoting dyer floors, and future nutritional supplementation can boost higher-quality horn tissue and denser keratinocyte proliferation.

Summary

Lameness has always been one of the major reasons for the culling of gilts and sows.

There are several causes of lameness, including osteochondrosis, bacterial infection, inflammation, trauma, and claw lesions.

Improving lameness factors can significantly improve longevity and herd productivity.


Mark E. Wilson

Mark earned his doctoral and a master’s degree from the University of Kentucky, and a bachelor’s degree from Iowa State University. He spent 11 years as a professor at the University of Minnesota (Waseca), coordinating the swine research at the Southern Experimental Station. He later served as the Director of Technical Service at United Feeds for nine years overseeing boar and sow research. He has also worked at Minitube of America as VP of Technology Transfer. Prior to that, Mark spent 13 years as part of the research and nutritional services team at Zinpro Corporation, and now has three years at Feedworks USA performing monogastric research and more. He is married, has three daughters and four grandchildren.